1. Field of the Invention
The present invention is related to a semiconductor device assembly, including a semiconductor device having a plurality of bond pads on the active surface thereof and a lead frame having a first portion of the plurality of lead fingers of the lead frame located below the inactive surface of the semiconductor device in a substantially horizontal plane and another portion of the plurality of lead fingers of the lead frame located substantially in the same horizontal plane as the active surface of the semiconductor device. Both plurality of lead fingers of the lead frame having their ends being located substantially adjacent the peripheral sides of the semiconductor device, rather than at the ends thereof.
2. State of the Art
High performance, low cost, increased miniaturization of components, and greater packaging density of integrated circuits have been and are goals in the electronics industry. Greater integrated circuit package density, for a given level of component and internal conductor density, is primarily limited by the space available for semiconductor device mounting and packaging. For lead frame mounted semiconductor devices, this limitation is a result of the conventional lead frame design, such conventional lead frame design inherently limits potential single-die package density because the die-attach paddle of the lead frame must be as large or larger than the semiconductor device secured thereto. The larger the semiconductor device, the less space (relative to size of the semiconductor device) that remains around the periphery of the die-attach paddle for bond pads for attendant wire bonding. Furthermore, the inner ends of the lead fingers of a lead frame provide anchor points for the lead fingers when the lead fingers and the die are encapsulated in plastic. These anchor points may be emphasized later as flanges or bends or kinks in the lead. Therefore, as the die size is increased in relation to the package size in ever decreasing size semiconductor packages, there is a corresponding reduction in the space along the sides of the package for the encapsulating plastic which joins the top and bottom portions of the molded plastic body at the mold part line and anchors to the leads. As the leads are subjected to the normal stresses of forming and assembly operations, the encapsulating plastic may crack, which may destroy the package seal and substantially increase the probability of premature semiconductor device failure.
One method of increasing integrated circuit density is to stack semiconductor dice vertically. U.S. Pat. No. 5,012,323 to Farnworth illustrates combining a pair of semiconductor devices mounted on opposing sides of a lead frame. An upper semiconductor device is back-bonded to the upper surface of the leads of the lead frame by a first adhesively coated, insulated film layer. The lower semiconductor device is face-bonded to the lower lead frame die-bonding region via a second, adhesively coated, insulative, film layer. The wire-bonding pads on both upper and lower semiconductor devices are interconnected with the ends of their associated lead extensions with gold or aluminum wires. The lower device needs to be slightly larger than the upper device in order that the lower die bonding pads are accessible from above through an aperture in the lead frame such that gold wire connections can be made to the lead extensions. However, this arrangement has a major disadvantage from a production standpoint, since the different size semiconductor devices require that different separate equipment produce the different dice or that the same equipment be switched over in different production runs to produce the different semiconductor devices. Moreover, the lead frame design employed by Farnworth employs long conductor runs between the die and the exterior of the package. Also, the lead frame configuration is specialized and rather complex.
U.S. Pat. No. 5,291,061 to Ball illustrates a multiple stacked semiconductor device that contains up to four such devices which does not exceed the height of current single semiconductor device packages. The low profile of the semiconductor device is achieved by close-tolerance stacking, which is made possible by a low-loop-profile wirebonding operation and thin adhesive layers between the stacked semiconductor devices. However, Ball secures all of the semiconductor devices to the same side of the lead frame, thereby increasing wire length. Moreover, Ball employs a die paddle to support the semiconductor device stack.
U.S. Pat. No. 4,862,245 to Pashby illustrates a "leads-over-chip" (LOC) configuration, wherein the inner lead ends of a standard dual-in-line package (DIP) lead frame configuration extend over and are secured to the active (upper) surface of the semiconductor device through a dielectric layer. The bond wire length is shortened by placing the inner lead ends in closer proximity to a central row of die bond pads, and the lead extensions purportedly enhance heat transfer from the semiconductor device. However, the Pashby LOC configuration, as disclosed, relates to mounting and bonding a single semiconductor device with the inner lead ends of the lead fingers to the surface of the semiconductor device.
U.S. Pat. No. 4,943,843 illustrates a semiconductor device having improved packaging adhesion of the lead fingers within the packaging resin by spreading leads on or near the non-circuit forming face of the semiconductor device thereby extending the lengths of the inner portions of the lead fingers on or under the semiconductor device. As illustrated in the '843 patent, the semiconductor device is of the type having bond pads located only on the ends thereof, not the peripheral sides of the semiconductor device or about the entire periphery of the semiconductor device.
U.S. Pat. No. 4,595,945 illustrates a lead frame to distribute power off a semiconductor device using a lead frame having the support paddle of the lead frame being split electrically to provide at least two conductor members that cross under the inactive surface of the semiconductor device. As illustrated, the semiconductor device is of the configuration type having bond pads located only on the ends thereof, not about the peripheral sides of the semiconductor chip or the periphery of the semiconductor device.
U.S. Pat. No. 5,554,886 illustrates a lead frame used to support a semiconductor device having a portion of the peripheral lead fingers of the lead frame extending along the peripheral sides of the semiconductor device and locally supporting the semiconductor chip therealong. However, no lead fingers are used which extend under the length of the inactive surface of the semiconductor chip to support the semiconductor device and are connected by wire bonding to the bond pads of the semiconductor device.
U.S. Pat. No. 5,557,143 illustrates a packaged semiconductor device assembly utilizing a plurality of leads. Such leads are arranged in an up and down staggered manner, an interval between ends of low stage leads in the package being narrower than a width of upper stage leads and ends of the lower stage leads in the package are positioned nearer to the semiconductor device pad than ends of the upper stage leads. However, none of the leads extend below the semiconductor device which is solely supported by the die paddle (pad).